On a Wednesday afternoon, members of the Aspen Athletic Club in Clive file into its spinning room. Each member approaches one of the room’s 30 bikes to the adjust the pedal-tension and the height of the seat.

As 5:45 p.m. rolls around, they mount their bikes. Music begins to play while they warm up. Soon, the overhead lights are turned off, and colored lights flash in the dark. The strong beat of the music pounds through the cyclists as instructor Jen Eagle-Fisher calls out to them, correcting their form or telling them to change positions to simulate the feel of biking up and down hills, jumping or riding on a flat surface. The students’ breathing speeds up, and their heart rates increase as they shift and sweat to the techno or metal music.

“You use your body to feel a hill,” Eagle-Fisher said when describing the experience. “You put your hands in different positions on the handlebars, change the position of your feet and how you move, using resistance and cadence to mimic outdoor cycling. A beginner and an elite athlete can be in the same class. Each can use the resistance and speed at which they feel comfortable. Well, not comfortable. We never want them to be comfortable.”

Eagle-Fisher, who is also Aspen’s group fitness director, says spinning is one of the most popular classes the fitness club offers. She says participants can burn up to 500 calories in the course of a 45-minute class. Other popular classes include Body Pump and Bosu.

Body Pump is a choreographed weightlifting program. A series of songs play, and each five-minute song features choreography that focuses on developing one area of the body, 10 areas in all. While one muscle group rests, another is worked.

Step classes, which were all the rage a few years ago, are making a comeback with Bosu. In Bosu, step exercises are performed on a half-ball. Exercisers must carefully maintain their balance while moving onto and off of the small, colorful domes.

“It stands for Both Sides Up,” Eagle-Fisher said. “[Students] get the normal step aerobic workout, but they also have to use their stabilizing muscles to stay on the platform.”

Janice Gutknect, group fitness director for Prairie Life Health & Fitness in West Des Moines, says spinning is one of the top classes for executives at her club, too.

“It’s popular with males and females,” she said. “It’s a good workout, because it’s high-intensity but low-impact.”

Other popular classes at Prairie Life are yoga-fusion classes, which combine yoga the stretching elements of yoga and the strength-increasing elements of Pilates, and the “kick-mix” classes, which Gutknect describes as “anything to do with kickboxing.”

Cardiovascular-kickboxing classes are tops at Fitness World West, too, according to fitness director Brent Havermann. He describes the classes as a mix of kicks and punches set to music. Another popular class at the West Des Moines gym is Box Aerobic.

“The members stand around punching-bags and they wear boxing gloves,” Havermann said. “They do steps, like shadowboxing, some cardio-moves and some dance moves. They hit the bag. Sometimes they carry big pads, and [their classmates] go around with gloves and hit the pads. The members chant and motivate each other.”

He says he sees executives flocking to yoga and pilates classes. Those classes are good for professionals, especially those less accustomed to exercising, because they increase lean muscle tissue without as much cardiovascular strain.

Also popular at Fitness World West is its Microfit system. When someone joins the gym, they go through a series of tests to record their blood pressure, weight, body fat percentage, strength, flexibility and aerobic capacity. Every few months, the tests are administered again. People often gain motivation by seeing their weight or body fat decrease. The measurements also help members choose the right exercise programs.

“Maybe they’ll find they’re gaining flexibility, but not strength,” Havermann said. “We can help them modify their exercise program to get the results they want. Or maybe someone has reached their goal weight, but now they want to tone their arms. Once they achieve their goals, this can help them set new ones.”